Café wall
Richard Gregory & Priscilla Heard; observed by Steve Simpson
Perfectly parallel mortar lines seem to slope.
Size & geometry / 1908
Fraser’s spiral
A spiral that is made entirely of circles.
TRY THIS
Trace a single dark-and-light cord around the image with your finger. It closes as a circle instead of spiraling into the center.
THE IMAGE IN THIS ARCHIVE
Trent Steel, from on original concept found by James Fraser in 1908.
Original file & attribution · Public domain
Original image downloaded from Wikimedia Commons; the downloaded file is unchanged. Gallery previews may be resized or converted to WebP; animated previews show the first frame.
Download imageFrequently asked questions
What is Fraser’s spiral?
A spiral that is made entirely of circles.
What should I look for in Fraser’s spiral?
Trace a single dark-and-light cord around the image with your finger. It closes as a circle instead of spiraling into the center.
What explains Fraser’s spiral?
The local tilts within each circular band bias the orientation you assign to the band as a whole. The circles are interpreted as curving inward even though their radii stay constant.
Another way to see it
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Ebbinghaus circles
Traditionally Hermann Ebbinghaus; popularized by E. B. Titchener
The neighbors change the size of the circle you see.